A structure has been conventionally known, in which: a pair of left and right front side frames are provided at a vehicle body front portion, or a pair of left and right rear side frames are provided at a vehicle body rear portion; and a bumper reinforcement extending in a vehicle width direction is attached to tip end portions of these side frames through a pair of left and right crash cans (also called crush boxes) capable of absorbing impact energy in collision.
The pair of crash cans are typically molded by a metal material. In vehicle collision, the pair of crash cans cause compression fracture in an axial direction to absorb impact energy transmitted to a vehicle interior.
It is also known that since the crash can is a large component, the crash can is constituted by a fiber-reinforced resin molded body for the purpose of a weight reduction of a vehicle body.
Examples of the reinforced fiber used as a reinforcing member include a glass fiber, a carbon fiber, and a metal fiber. The fiber-reinforced resin is formed by combining the reinforced fibers with a base material (matrix).
According to such fiber-reinforced resin, the reinforced fibers take charge of dynamic characteristics, such as strength, and the base material resin takes charge of a stress transmission function between the fibers and a fiber protection function.
Especially, carbon fiber resin (Carbon-Fiber-Reinforced-Plastic: CFRP) has both high specific strength (strength/specific gravity) and high specific rigidity (rigidity/specific gravity), so to speak, both lightness and strength or rigidity. Therefore, the carbon fiber resin is widely used as a structural material for aircrafts, vehicles, and the like.
An impact absorbing member of PTL 1 is an impact absorbing member made of a composite material containing synthetic resin and carbon fibers, and an impact fracture temperature of the impact absorbing member is set to a range of −15° C. or more and +50° C. or less of a glass transition temperature of the resin. With this, high energy absorbing performance is secured.
PTL 1 discloses that this impact absorbing member is formed in a tubular shape, a columnar shape, a closed-section prism shape, or the like.
Performance required for impact absorbing members is a large energy absorption amount (hereinafter referred to as an EA amount) and a stable absorption of impact energy by progressive fracture in which compression fracture proceeds progressively.